g it is best to
plough in the crop when it is in flower, as no additional benefit is
gained by allowing it to ripen, seeing that no further absorption of
fertilising ingredients takes place after the period of flowering.

_Influence of excessive Manuring of Crops._

The influence of large quantities of manures is seen in the case of
certain root crops. It is found, in such a case, that while the roots
are larger, they are more watery in composition and of less nutritive
value. Again, it seems to be a fact pretty generally known to practical
men, that nitrate of soda seems to have a bad effect on the quality of
hay. It would seem, further, that the influence of nitrogenous
fertilisers on cereals is to increase the percentage of nitrogen in the
grain, but that they have no such influence in the case of leguminous
crops. Phosphatic manures, on the other hand, in the case of leguminous
crops, seem to have the effect of diminishing the amount of nitrogen in
the seed.

FOOTNOTES:

[241] Though not necessarily at the same time or to each succeeding
crop. There may be comparatively long intervals between the applications
of farmyard manure in many cases.

[242] Of course what is meant here is the direct influence of such
manures. Their indirect value may be shown in the soil by the increased
crop residues they give rise to.

[243] This is very concisely and clearly put in Mr Warington's admirable
'Chemistry of the Farm.'

CHAPTER XXIII.

MANURING OF THE COMMON FARM CROPS.

In this chapter we shall attempt to summarise briefly the results of
experiments on the manuring of some of the commoner crops, and we shall
start with the manuring of cereals.

CEREALS.

As we have already pointed out, a certain similarity in the manurial
requirements of the different members of this class exists. They are
characterised, for one thing, by the comparatively small quantity of
nitrogen they remove from the soil--less than either leguminous or root
crops. Of this nitrogen the larger proportion--amounting to
two-thirds--is contained in the grain, the straw only containing about a
quarter of the total amount of nitrogen in the plant. The amount of
phosphoric acid they remove from the soil is not much less than that
removed by the other two classes of crops; but this, again, is also
chiefly in the grain. It is on this account that the cereals may be
regarded, in a sense, as exhaustive crops, seeing that the grain is
al